1. Field of Invention
This invention relates to holography and more particularly to synthetic focused image holograms.
2. Description of the Prior Art
A thermoplastic recording medium, for recording a hologram of an image, typically includes a thermoplastic layer on a photoconductor layer. The thermoplastic is a dielectric which becomes soft, and therefore deformable, in response to an application of heat. The photoconductor is a dielectric having a conductivity that increases with the intensity of light transmitted thereto.
To record what is known as a synthetic focused image halogram, a uniform voltage is applied across the thermoplastic and the photoconductor, thereby charging the thermoplastic and the photoconductor. The uniform voltage establishes uniform electric fields within the photoconductor and the thermoplastic. After the uniform electric fields are established, the charging is discontinued.
The charged photoconductor is exposed to a pair of beams of coherent light, the coherent light beams interacting upon the photoconductor to form a uniform interference pattern. Concurrent with the exposure to the coherent light, the photoconductor is exposed to a white light image. Within the photoconductor, there is a pattern of conduction corresponding to the white light image superimposed upon the interference pattern. The conduction causes a decrease of the intensity of the electric field within the photoconductor in a corresponding pattern.
After the concurrent exposures, the uniform voltage is applied across the thermoplastic and the photoconductor to recharge them. The recharging causes the intensity of the electric field within the thermoplastic to be representative of a desired diffraction grating comprising the synthetic focused image hologram.
The surfaces of the thermoplastic are attracted to each other by an electrostatic force proportional to the square of the intensity of the electric field within the thermoplastic. When the electric field is representative of the desired diffraction grating, the thermoplastic is softened by an application of heat. The force of attraction deforms the thermoplastic, the deformation comprising the synthetic focused image hologram.
In the prior art, a complex arrangement of optical elements, including a laser source of coherent light, is used to record the synthetic focused image hologram. It is desirable to record the synthetic focused image hologram with a simple arrangement of optical elements that does not include the laser source.